The present invention generally relates to hand held dispensers for mixing and dispensing reactive chemical foam compositions, such as curable polyurethane foams, useful for a number of end use applications. More particularly, it relates to a new and improved foam dispensing gun having a receiving carrier portion and a removable dispenser cartridge mounted in the carrier in sealed movable relation therewith to provide primary sealing external to the cartridge mixing chamber for controlling on/off flow of the pressurized components to provide improved sealing and dispensing performance and extended cartridge service life.
Reactive chemical foam compositions, such as curable polyurethane foams, are presently well known and used in a number of different applications. The curable foam compositions typically comprise a two-part composition and, in the case of polyurethane foams, one part of the composition includes a polyol component and the other part includes an isocyanate component. Chemical blowing agents, curing agents, catalysts or accelerators, as well as other modifying additives, may be incorporated in one or both of the component parts. These two-parts of the foaming composition are separately stored in different containers until use.
For use, the two parts of the composition are rapidly mixed together. A rapid exothermic cross linking reaction and foam expansion commences which ultimately yields a low or a high density, relatively high load bearing urethane rigid foam. Expanding chemical foams are useful in such applications as thermal insulation, in floatation, in coatings and, more recently, the foams have been used in the specialty packaging industry. The mixing of the polyol and isocyanate components must occur at a proper flow ratio and mix under rapid and sufficient impingement mixing conditions for a final acceptable product to be obtained. In the past, particularly in the precise field of building thermally insulated containers for refrigeration units or shipping containers, foam components were dispensed using static mixing equipment. The static mixers relied upon dangerous organic solvents such as methylene chloride to rinse and flush the dispenser's mixing chamber after use. Nowadays the environmental hazards of using these solvent materials renders static mixers no longer suitable for commercial foam applications and contexts.
More recently, the urethane components including the resin or polyol component and the isocyanate component are stored under pressure in returnable containers which are attached to solventless hand held impingement mixing and discharge dispensers by means of various hoses and couplings. The dispensers include a trigger operated system designed to permit the two-parts of the composition to flow into a mixing chamber wherein the products are rapidly mixed to form a reactive and expanding chemical foam composition which exits through the open end of the cartridge. In prior art dispensers, the component delivery systems extending from the pressurized storage tanks into the dispenser cartridge of the dispenser are typically multi-part systems and the potential for leakage at every joint therealong exists in the high pressure impingement mixing environment.
In these dispensers, the components are mixed by direct or indirect impingement with each other under conditions of high pressure to ensure thorough mixing. The design of the mixing cartridges has become a matter of concern in the art. The component parts of the foam composition are highly chemically reactive and begin to form cured polymeric products within a matter of seconds. Premature leaking and mixing of the components within the cartridges is a serious and major concern because leakage results in undesirable curing in the cartridge causing blockage and jamming to the cartridge in use. As a result, the cartridges have to be frequently maintained or replaced at considerable expense. Providing adequate seals within the cartridge assemblies in the high pressure environment has been another major problem to those in the art.
Prior art foam dispensers are known, for example, from U.S. Pat. No. 4,469,251, U.S. Pat. No. 4,568,003 U.S. Pat. No. 4,993,596 and from copending application Ser. No. 771,802, filed Oct. 17, 1991. In accordance with these prior dispenser arrangements, a detachable cartridge includes a mixing chamber defined in a central bore within a polymeric insert. Typically, the polymeric insert is formed of a TEFLON.RTM. material because the reactive foam composition and its end products are not adherent to the TEFLON.RTM. surfaces along the interior of the bore.
More particularly, the TEFLON.RTM. insert has a central bore extending longitudinally therethrough. A plurality of openings extend through a sidewall of the insert in communication with the bore for supplying the organic resin and the isocyanate components into the mixing chamber. A valving rod is provided in a slidable interference fit within the bore to control the flow of organic polyol resin component and isocyanate component from the side openings into the mixing chamber and discharge of the foam therefrom. Secondly, the valving rod serves to clean the mixing chamber on the reverse stroke as it reseals the material supply orifices within the insert. Each of the prior art dispensers attempt to provide a primary seal to the flow of the components along the curved outer circumferential surface of the valving rod. To provide a reliable surface to surface seal along two curved cylindrical surfaces is difficult or impossible to maintain in the medium to high pressure context. Dimensions between the valving rod and the dispenser cartridge insert aperture are critical to maintain fluid tight conditions and must be kept to extremely close tolerances.
Although the inserts exhibit non-adherent surface characteristics, TEFLON.RTM. materials are notorious for suffering from hysteresis, wear or cold flow dimensional instability. Cold flow of the TEFLON.RTM. material causes a distortion or a change in the critical dimensions of the central bore and the side openings of the insert. In addition, friction and wear between the TEFLON.RTM. insert and the valving rod also contribute to a loss of critical sealing dimensions for these parts. Over time this often results in a loss of the interference fit between the valving rod and the insert.
More particularly, with each activation of the valving rod, a minor film of foam product and components coats the rod. As the coating builds up on the rod, the effective diameter of the rod increases. The foam build up on the rod increases the stresses on the insert in use, leading to cold flow deformation, loss of tolerances and a loss of sealing between the rod, the core aperture and the side openings in the dispenser cartridge. This results in leakage and cross-over contamination, valving rod jamming and blockage failures in the dispenser. As a result, the ability of the valving rod to effectively seal the openings to thereby prevent leakage of the reactive components into the mixing chamber is lost. Cross-overs, blockage and leakage ultimately cause obstruction within the mixing chamber which renders the dispensing cartridge generally inoperable.
In an effort to overcome the tendency of the valving inserts to undergo cold flow deformation with a consequent loss in sealing and usefulness, conventional dispenser cartridges or cartridges have been provided with means for applying a constant axial and radial compressive load against the polymeric insert member. Applying constant radial and axial loads on the insert tends to reduce some of the cold flow induced failures of the prior art nozzles. Applying a constant radial and axial load increases frictional forces developed between the valve insert and the valving rod which tends to increase the residual stresses on the insert responsible for cold flowing. Presently, the frequency of failure is still undesirably high in view of the expense associated with replacement, downtime interruptions in production and repair of the mixing chamber/dispensing cartridges. For example, a typical commercial impingement mixing hand held foam dispenser may generally only be subjected to approximately 2,000 to 3,000 dispensing activation cycles before cartridge failure is experienced.
The deficient seal-wearing performance of the prior art valving rod and TEFLON.RTM.sleeve or bushing sealing arrangements are expected to become even more significant in the future. More particularly, the arrangement of two component entry ports set at an angled orientation with respect to each other and sealed along the surfaces of the valving rod is difficult enough for two component ports, however, modern industry regulations are presently requiring reduction or elimination of halohydrocarbon blowing agents such as CFCs, and the new substitute blowing agent systems require the addition of still a third or fourth chemical component to the impingement mixing process. This will require that structural modifications be made to the cartridge, such as making the chemical component entry ports of a larger size or diameter, as well as adding multiple ports. These modifications will only exacerbate current wear-performance problems associated with the valving rod TEFLON.RTM. sleeve sealing arrangements currently in use.
Accordingly, to overcome the disadvantages of the prior art dispensers, it is an object of the present invention to provide new and improved foam dispensers including a dispenser cartridge design characterized by prolonged or extended use lives of more than 20,000 activation/dispense cycles.
It is another object of the present invention to provide a new and improved dispenser cartridge which does not rely upon a valving rod for providing a fluid tight seal for the reactant materials, and which does not depart from a simple low cost design.
It is a further object of the present invention to provide a dispenser cartridge arrangement which relies upon dependable external face seals to provide the primary sealing mechanism in connection with opening and closing the material flow ports of the reactive chemical components.
It is still another object of the present invention to provide a new and improved dispenser cartridge assembly wherein the valving rod primarily performs the function of purging the impingement mixing chamber of residues and provides a secondary redundant seal for the chemical component flow ports.
It is a further object of the present invention to provide a new and improved dispenser and cartridge capable of achieving higher outputs without departure from the traditional low-output design and cost.
It is another object of the present invention to provide a ne and improved foam dispenser and cartridge assembly which achieves high output levels while maintaining minimal orifice diameters in order to reduce component cross-over tendencies.
It is still another object of the present invention to provide a high output foam dispenser which subdivides the main component streams into multiple streams and separately impinges these streams at multiple sites in the mixing chamber to maximize turbulent interaction and thereby provide improved foaming performance and quality.
It is still a further object of the present invention to provide a new and improved dispenser cartridge including multiple orifices to accommodate varying numbers of components required for mixing or to increase overall output of the foam dispenser.
It is still another object of the present invention to provide multiple orifice options in a dispenser cartridge and carrier arrangement to permit the cartridge to dispense a number of variable component ratio formulations.